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Patented Sept. 10, 1929.

UNITED STATES PATENT OFFICE.

PROCESS OF REDUCING ZINC ORES.

No Drawing. Application filed December 1. 1926, Serial No. 152,070, and in Germany October 23, 1926.

This invention relates to a process of reducing zinc ores which consists in reducing the ores with carbide in a nitrogen-current. According to this process non-calcined zinc sulphide ore can be converted directly into metallic zinc, only very little quantities of zinc (0.5% or less) remaining in the slags.

The conversion of zinc sulphide ores takes place according to the equation ZnS MeG Zn+ MeS 20 As shown by this equation metallic sulphides are obtained in this process as byproducts. The process is, therefore, specially important for the production of barium sulphide and calcium sulphide as by-products. The products were hitherto obtained only as main products at the reaction of the corresponding sulphates.

The nitrogen serves as protecting atmosphere and prevents oxidation of the corresponding sulphide to sulphate. Instead of nitrogen any other gas may be used which does not have a disturbing influence upon the reaction.

If calcium carbide is used for carrying out the process, residues which contain calcium sulphide are produced at the reduction of sulphide zinc ores. These residues may serve, eventually with the addition of carbon, for the production of carbide or for the nitration of carbide producing mixtures. They are especially adapted for this purpose as they contain in an extremely fine distribution, the iron which exists in the zinc ore, and in a freshly reduced state, this 1 facilitating the generation of carbide from sulphide-containing mixtures.

The process may he carried out in any 40 known furnace which is suited for the reduction of zinc ores with carbide. The known muffle furnaces are of course closed, and in addition thereto, it is obviously only necessary to provide an inlet and outlet for the stream of nitrogen. The invention depends upon no particular furnace construction and many suitable modifications of furnace structure will be apparent to those familiar with the art.

The principles of the invention may be applied to various mixtures and charges containing numerous variations as to quantities and ratios of the reacting substances, and the following is mentioned by way of example only.

Approximately equal parts of, say, 72% carbide and 45% ground zinc sulphide, containing possibly about 5% of a dry flux such as an alkaline chloride, are poured into a zinc inullle furnace which may be heated indirectly or directly by means of electric resistance and which is provided with a zinc lined gas inlet and outlet. The air originally in the muflle is expelled by the stream of nitrogen which is passed through the furnace. The temperature is gradually raised to about 1200 C. At about 700 C. the reduction process begins but, of course, becomes more vigorous with a rising temperature which may be easily regulated by avariation of the supply of nitrogen. About 90% of the zinc will be secured in metallic form, and the remainder, except for some few tenths per cent which will be left in the residue, will be obtained as dust. The residue contains, besides small amounts of zinc varying from one-tenth .to five-tenths per cent, a high grade" calcium sulphide. Further heating of the calcium sulphide to a substantially higher temperature with the admission of nitrogen will form a product containing about 12% to 14% of nitrogen.

I claim 1. The process for the reduction of zinc ores by carbide, characterized by the fact that the ores are reduced by carbide in a stream of nitrogen.

2. The process of reducing a zinc sulphide ore which comprises forming a mixture of the ore and a carbide, heating themixture and reducing the ore by the carbide in the presence of a stream of nitrogen.

In testimony whereof I aflix my signature.

HERBERT 'WITTEK. 

